The present invention relates to perfusion and specifically to the therapeutic use of hemoglobin in low doses to increase perfusion.
Perfusion is supplying an organ or tissue with oxygen and nutrients via blood or a suitable fluid. Perfusion is essentially the flow of fluid to tissues and organs through arteries and capillaries. Flow may be expressed as the ratio of pressure to resistance. If adequate oxygen and nutrients are not reaching tissues and organs, therapies to improve perfusion may be employed.
Current management of hypotension, and its concurrent reduction in perfusion of tissues and organs, consists of the administration of (i) vasopressors, (ii) positive inotropic agents, and/or (iii) vascular volume expanders depending on the underlying etiology. Hypotension secondary to actual or relative hypovolemia, which also reduces perfusion, initially is managed by administration of crystalloid or colloid solutions and/or blood products.
Therapeutics which increase blood pressure are employed in an attempt to increase perfusion. Vasopressor agents such as epinephrine, phenylephrine, metaraminol and methoxamine cause contraction of the muscles of capillaries and arteries. This increases resistance to the flow of blood and elevates blood pressure. However, these drugs are not optimal for increasing perfusion. They pose a risk of inducing excessive blood pressure; are known to cause arrhythmias; require intraarterial pressure monitoring; and tissue sloughing and necrosis may result if extravasation occurs. Moreover, vasopressor agents may actually decrease the flow of oxygen and nutrients to tissues and organs. If the constriction of the capillaries and arteries increases resistance in proportion to the increase in blood pressure, the net flow, i.e., perfusion, will be unchanged. However, large increases in resistance result in decreased flow. At best a localized increase in perfusion in large vessels occurs while the flow in capillaries is reduced. Indeed, vasopressor agents have been reported to result in decreased perfusion of vital organs. Moreover, because vasopressors increase venous pressure as well as arterial pressure, and, therefore can limit optimal fluid administration, such agents generally are given only after sufficient volume replacement with an appropriate fluid or blood. W. C. Shoemaker, A. W. Fleming, "Resuscitation of the Trauma Patient; Restoration of Hemodynamic Functions Using Clinical Algorithms," Ann. Emerg. Med., 15:1437 (1986). Dopamine hydrochloride is an inotropic agent used in the treatment of shock to increase blood pressure. It suffers from the drawbacks noted above for vasopressor agents. In addition, it has a very small therapeutic window. Because the dose/response is extremely sensitive, dopamine must be carefully titrated, and invasive monitoring (arterial line) is required.
A class of therapeutics known as plasma expanders or volume replacements may be used to increase perfusion where significant blood loss has occurred. In this therapy perfusion is increased by administering volume replacement fluids such as albumin, Ringer's lactate, saline, or dextran solutions. A decrease in blood volume causes a decrease in pressure. By restoring the volume, some pressure, and thus flow can be restored. In addition, these solutions do not carry oxygen or nutrients. So, while flow may be restored, oxygen delivery to the tissues is reduced because oxygen and nutrient content of the blood is diluted. Hemodilution is beneficial in that it reduces the viscosity of the blood, thus reducing resistance and increasing flow. But without the necessary oxygen and nutrients, this therapy is not an optimal treatment for significant blood loss.
Volume replacement with whole blood is currently the most efficacious treatment when there has been significant blood loss. However, this cannot be used in a pre-hospital setting and its use requires a twenty minute wait for matching and typing, assuming a donor blood supply is available. Studies have also shown that the increased viscosity associated with infusion of blood may limit capillary blood flow. K. M. Jan, J. Heldman, and S. Chen, "Coronary Hemodynamics and Oxygen Utilization after Hematocrit Variations in Hemorrhage," Am. J. Physiol., 239:H326 (1980). There is also the risk of viral (hepatitis and/or HIV) or bacterial infection from transfused blood.
Hemoglobin solutions have been under investigation as oxygen carrying plasma expanders or blood substitutes for more than fifty years. While no hemoglobin solution is currently approved for use clinically, they are intended to be used to replace blood lost through hemorrhage. Their effectiveness as oxygen carriers has been demonstrated. However, their potential toxicity has been the focus of much research.
Even small amounts of stroma (cell membrane) in hemoglobin solutions appear to be toxic. R. W. Winslow, "Hemoglobin-based Red Cell Substitutes," The Johns Hopkins University Press, Baltimore (1992). Such toxic effects include renal vasoconstriction and decreased renal flow as well as hypertension and bradycardia. In 1967 Rabiner utilized rigorous purification techniques to develop stroma-free hemoglobin which has prevented some of the toxic effects encountered with prior hemoglobin solutions.
In connection with toxicity studies for hemoglobin solutions researchers noted an elevation in blood pressure as early as 1934. W. R. Amberson, J. Flexner, F. R. Steggerada et al., "On Use of Ringer-Locke Solutions Containing Hemoglobin as a Substitute for Normal Blood in Mammals," J. Cell Comp. Physiol., 5:359 (1934). Current toxicity studies of hemoglobin solutions continue to note a pressor effect. For example, the replacement of blood with various bovine hemoglobin solutions in rabbits in a 1988 study was characterized by significant hemodynamic instability, with fluctuations of blood pressure and heart rate, and severe tachypinea. Of the various hemoglobin solutions tested in this study, the purest (which comprised cross-linked hemoglobin) showed the least toxicity, but nevertheless "did produce a hypertensive reaction suggestive of a systemic vasoconstrictor effect." M. Feola, J. Simoni, P. C. Canizaro, R. Tran, G. Raschbaum, and F. J. Behal, "Toxicity of Polymerized Hemoglobin Solutions," Surg. Gynecol. Obstet., 166:211 (1988). In 1975 Rabiner reported on the work of a Russian researcher who noted a beneficial effect following administration of 200-400 ml of a 3% hemoglobin solution heavily contaminated with stroma lipid to each of 20 trauma patients, in that there was a stabilization of blood pressure. S. F. Rabiner, "Hemoglobin Solution as a Plasma Expander," Fed. Proc., 34:1454 (1975). In 1949 Amberson et al. reported that the administration of 2300 ml of a 6% hemoglobin solution (225 grams hemoglobin) restored blood pressure to normal in a patient who had suffered significant blood loss through hemorrhage. W. R. Amberson, J. J. Jennings, and C. M. Rhode, "Clinical Experience with Hemoglobin-Saline Solutions," J. Appl. Physiol., 1:469 (1949).
Although methods of measurement and reporting have been inconsistent, an increase in blood pressure and a fall in heart rate are frequently reported findings associated with administration of a variety of hemoglobin solutions in animals and man. Those researchers noting the pressor effect of solutions include G. A. H. Buttle, A. Kekwick, and A. Schweitzer, "Blood Substitutes in Treatment of Acute Hemorrhage," Lancet, 2:507 (1940). J. H. Miller and R. K. McDonald, "The Effect of Hemoglobin in Renal Function in the Human," J. Clin. Invest., 30:1033 (1951). C. Elia, H. J. Sternberg, A. Greenburg, and G. W. Peskin, "Stroma-free Hemoglobin in the Resuscitation of Hemorrhagic Shock," Surg. Forum, 25:201 (1974). G. S. Moss, R. DeWoskin, A. L. Rosen, H. Levine, and C. K. Palani, "Transport of Oxygen and Carbon Dioxide by Hemoglobin-saline Solution in the Red Cell Free Primate," Surg. Gynecol. Obstet., 142:357 (1976). J. P. Savitsky, J. Doczi, J. Black, and J. D. Arnold, "A Clinical Safety Trial of Stroma-free Hemoglobin," Clin. Pharmacol. Ther., 23:73 (1978). P. E. Keipert and T. M. S. Chang, "Pyridoxylated Polyhemoglobin as a Red Cell Substitute for Resuscitation of Lethal Hemorrhagic Shock in Conscious Rats," Biomater. Med. Devices Artif. Organs, 13:1 (1985). F. H. Jesch, W. Peters, J. Hobbhahn, M. Schoenberg, and K. Messmer, "Oxygen-transporting Fluids and Oxygen Delivery with Hemodilution," Crit. Care Med., 10:270 (1982).
Two early animal studies in which hemoglobin solutions were administered following controlled hemorrhage and occlusion of the left coronary artery demonstrated improved myocardial blood flow compared to autologous blood or dextran. G. P. Biro and D. Beresford-Kroeger, "The Effect of Hemodilution with Stroma-free Hemoglobin and Dextran on Collateral Perfusion of Ischemic Myocardium in the Dog," Am. Hrt. J., 99:64 (1980). M. Feola, D. Azar, and L. Wiener, "Improved Oxygenation of Ischemic Myocardium by Hemodilution with Stroma-free Hemoglobin Solution," Chest. 75:369 (1979). Both of these studies were exchange transfusions (1:1 or 2:1) of very large doses of hemoglobin.
Renal complications frequently have been associated with use of high doses of hemoglobin solutions. Oliguria and decreased renal flow have been a common finding, although improved modifications of hemoglobin appear to have somewhat ameliorated this problem. N. I. Birndorf and H. Lopas, "Effect of Red Cell Stroma-free Hemoglobin Solution on Renal Function in Monkeys," J. Appl. Physiol., 29:573 (1970). M. Relihan, R. E. Olsen, and M. S. Litwin, "Clearance Rate and Effect on Renal Function of Stroma-free Hemoglobin Following Renal Ischemia," Ann. Surg., 176:700 (1972). Other reactions such as fever, chills, flushing, nausea, and chest and abdominal pain are often experienced.
In sum, hemoglobin solutions at high doses in high volume administered as oxygen carrying blood substitutes have been reported to increase blood pressure, and this effect has been characterized alternately as toxic or potentially beneficial.
Applicants have now discovered that, surprisingly, low doses of hemoglobin in small volumes may be administered therapeutically to rapidly increase perfusion.